/**
 * Copyright (C) 2006 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.azeckoski.reflectutils.refmap;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Starts a background thread that cleans up after reclaimed referents.
 *
 * @author Bob Lee (crazybob@google.com)
 */
class FinalizableReferenceQueue extends ReferenceQueue<Object> {

   private static final Logger logger =
      Logger.getLogger(FinalizableReferenceQueue.class.getName());

   private FinalizableReferenceQueue() {}

   @SuppressWarnings("unchecked")
   void cleanUp(Reference reference) {
      try {
         ((FinalizableReference) reference).finalizeReferent();
      } catch (Throwable t) {
         deliverBadNews(t);
      }
   }

   void deliverBadNews(Throwable t) {
      logger.log(Level.SEVERE, "Error cleaning up after reference.", t);
   }

   void start() {
      Thread thread = new Thread("FinalizableReferenceQueue") {
         public void run() {
            while (true) {
               try {
                  cleanUp(remove());
               } catch (InterruptedException e) { /* ignore */ }
            }
         }
      };
      thread.setDaemon(true);
      thread.start();
   }

   static final ReferenceQueue<Object> instance = createAndStart();

   static FinalizableReferenceQueue createAndStart() {
      FinalizableReferenceQueue queue = new FinalizableReferenceQueue();
      queue.start();
      return queue;
   }

   /**
    * Gets instance.
    */
   public static ReferenceQueue<Object> getInstance() {
      return instance;
   }
}
